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/*
 * Copyright 2013 Twitter, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.aoju.bus.http.metric.http;

import org.aoju.bus.core.io.BufferSink;
import org.aoju.bus.core.io.ByteString;
import org.aoju.bus.core.lang.Normal;

import java.io.ByteArrayOutputStream;
import java.io.IOException;

/**
 * 这个类最初是由以下类组成的<a href="https://github.com/twitter/hpack">Twitter Hpack</a>.
 *
 * <ul>
 *     <li>{@code com.twitter.hpack.HuffmanEncoder}</li>
 *     <li>{@code com.twitter.hpack.HuffmanDecoder}</li>
 *     <li>{@code com.twitter.hpack.HpackUtil}</li>
 * </ul>
 *
 * @author Kimi Liu
 * @version 6.5.0
 * @since Java 17+
 */
public class Huffman {

    private static final int[] CODES = {
            0x1ff8, 0x7fffd8, 0xfffffe2, 0xfffffe3, 0xfffffe4, 0xfffffe5, 0xfffffe6, 0xfffffe7, 0xfffffe8,
            0xffffea, 0x3ffffffc, 0xfffffe9, 0xfffffea, 0x3ffffffd, 0xfffffeb, 0xfffffec, 0xfffffed,
            0xfffffee, 0xfffffef, 0xffffff0, 0xffffff1, 0xffffff2, 0x3ffffffe, 0xffffff3, 0xffffff4,
            0xffffff5, 0xffffff6, 0xffffff7, 0xffffff8, 0xffffff9, 0xffffffa, 0xffffffb, 0x14, 0x3f8,
            0x3f9, 0xffa, 0x1ff9, 0x15, 0xf8, 0x7fa, 0x3fa, 0x3fb, 0xf9, 0x7fb, 0xfa, 0x16, 0x17, 0x18,
            0x0, 0x1, 0x2, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x5c, 0xfb, 0x7ffc, 0x20, 0xffb,
            0x3fc, 0x1ffa, 0x21, 0x5d, 0x5e, 0x5f, 0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68,
            0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70, 0x71, 0x72, 0xfc, 0x73, 0xfd, 0x1ffb, 0x7fff0,
            0x1ffc, 0x3ffc, 0x22, 0x7ffd, 0x3, 0x23, 0x4, 0x24, 0x5, 0x25, 0x26, 0x27, 0x6, 0x74, 0x75,
            0x28, 0x29, 0x2a, 0x7, 0x2b, 0x76, 0x2c, 0x8, 0x9, 0x2d, 0x77, 0x78, 0x79, 0x7a, 0x7b, 0x7ffe,
            0x7fc, 0x3ffd, 0x1ffd, 0xffffffc, 0xfffe6, 0x3fffd2, 0xfffe7, 0xfffe8, 0x3fffd3, 0x3fffd4,
            0x3fffd5, 0x7fffd9, 0x3fffd6, 0x7fffda, 0x7fffdb, 0x7fffdc, 0x7fffdd, 0x7fffde, 0xffffeb,
            0x7fffdf, 0xffffec, 0xffffed, 0x3fffd7, 0x7fffe0, 0xffffee, 0x7fffe1, 0x7fffe2, 0x7fffe3,
            0x7fffe4, 0x1fffdc, 0x3fffd8, 0x7fffe5, 0x3fffd9, 0x7fffe6, 0x7fffe7, 0xffffef, 0x3fffda,
            0x1fffdd, 0xfffe9, 0x3fffdb, 0x3fffdc, 0x7fffe8, 0x7fffe9, 0x1fffde, 0x7fffea, 0x3fffdd,
            0x3fffde, 0xfffff0, 0x1fffdf, 0x3fffdf, 0x7fffeb, 0x7fffec, 0x1fffe0, 0x1fffe1, 0x3fffe0,
            0x1fffe2, 0x7fffed, 0x3fffe1, 0x7fffee, 0x7fffef, 0xfffea, 0x3fffe2, 0x3fffe3, 0x3fffe4,
            0x7ffff0, 0x3fffe5, 0x3fffe6, 0x7ffff1, 0x3ffffe0, 0x3ffffe1, 0xfffeb, 0x7fff1, 0x3fffe7,
            0x7ffff2, 0x3fffe8, 0x1ffffec, 0x3ffffe2, 0x3ffffe3, 0x3ffffe4, 0x7ffffde, 0x7ffffdf,
            0x3ffffe5, 0xfffff1, 0x1ffffed, 0x7fff2, 0x1fffe3, 0x3ffffe6, 0x7ffffe0, 0x7ffffe1, 0x3ffffe7,
            0x7ffffe2, 0xfffff2, 0x1fffe4, 0x1fffe5, 0x3ffffe8, 0x3ffffe9, 0xffffffd, 0x7ffffe3,
            0x7ffffe4, 0x7ffffe5, 0xfffec, 0xfffff3, 0xfffed, 0x1fffe6, 0x3fffe9, 0x1fffe7, 0x1fffe8,
            0x7ffff3, 0x3fffea, 0x3fffeb, 0x1ffffee, 0x1ffffef, 0xfffff4, 0xfffff5, 0x3ffffea, 0x7ffff4,
            0x3ffffeb, 0x7ffffe6, 0x3ffffec, 0x3ffffed, 0x7ffffe7, 0x7ffffe8, 0x7ffffe9, 0x7ffffea,
            0x7ffffeb, 0xffffffe, 0x7ffffec, 0x7ffffed, 0x7ffffee, 0x7ffffef, 0x7fffff0, 0x3ffffee
    };

    private static final byte[] CODE_LENGTHS = {
            13, 23, 28, 28, 28, 28, 28, 28, 28, 24, 30, 28, 28, 30, 28, 28, 28, 28, 28, 28, 28, 28, 30,
            28, 28, 28, 28, 28, 28, 28, 28, 28, 6, 10, 10, 12, 13, 6, 8, 11, 10, 10, 8, 11, 8, 6, 6, 6, 5,
            5, 5, 6, 6, 6, 6, 6, 6, 6, 7, 8, 15, 6, 12, 10, 13, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
            7, 7, 7, 7, 7, 7, 7, 7, 7, 8, 7, 8, 13, 19, 13, 14, 6, 15, 5, 6, 5, 6, 5, 6, 6, 6, 5, 7, 7, 6,
            6, 6, 5, 6, 7, 6, 5, 5, 6, 7, 7, 7, 7, 7, 15, 11, 14, 13, 28, 20, 22, 20, 20, 22, 22, 22, 23,
            22, 23, 23, 23, 23, 23, 24, 23, 24, 24, 22, 23, 24, 23, 23, 23, 23, 21, 22, 23, 22, 23, 23,
            24, 22, 21, 20, 22, 22, 23, 23, 21, 23, 22, 22, 24, 21, 22, 23, 23, 21, 21, 22, 21, 23, 22,
            23, 23, 20, 22, 22, 22, 23, 22, 22, 23, 26, 26, 20, 19, 22, 23, 22, 25, 26, 26, 26, 27, 27,
            26, 24, 25, 19, 21, 26, 27, 27, 26, 27, 24, 21, 21, 26, 26, 28, 27, 27, 27, 20, 24, 20, 21,
            22, 21, 21, 23, 22, 22, 25, 25, 24, 24, 26, 23, 26, 27, 26, 26, 27, 27, 27, 27, 27, 28, 27,
            27, 27, 27, 27, 26
    };

    private static final Huffman INSTANCE = new Huffman();
    private final Node root = new Node();

    private Huffman() {
        buildTree();
    }

    public static Huffman get() {
        return INSTANCE;
    }

    void encode(ByteString data, BufferSink sink) throws IOException {
        long current = 0;
        int n = 0;

        for (int i = 0; i < data.size(); i++) {
            int b = data.getByte(i) & 0xFF;
            int code = CODES[b];
            int nbits = CODE_LENGTHS[b];

            current <<= nbits;
            current |= code;
            n += nbits;

            while (n >= 8) {
                n -= 8;
                sink.writeByte(((int) (current >> n)));
            }
        }

        if (n > 0) {
            current <<= (8 - n);
            current |= (0xFF >>> n);
            sink.writeByte((int) current);
        }
    }

    int encodedLength(ByteString bytes) {
        long len = 0;

        for (int i = 0; i < bytes.size(); i++) {
            int b = bytes.getByte(i) & 0xFF;
            len += CODE_LENGTHS[b];
        }

        return (int) ((len + 7) >> 3);
    }

    byte[] decode(byte[] buf) {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        Node node = root;
        int current = 0;
        int nbits = 0;
        for (int i = 0; i < buf.length; i++) {
            int b = buf[i] & 0xFF;
            current = (current << 8) | b;
            nbits += 8;
            while (nbits >= 8) {
                int c = (current >>> (nbits - 8)) & 0xFF;
                node = node.children[c];
                if (null == node.children) {
                    // 终端节点
                    baos.write(node.symbol);
                    nbits -= node.terminalBits;
                    node = root;
                } else {
                    // 非终结符节点
                    nbits -= 8;
                }
            }
        }

        while (nbits > 0) {
            int c = (current << (8 - nbits)) & 0xFF;
            node = node.children[c];
            if (null != node.children || node.terminalBits > nbits) {
                break;
            }
            baos.write(node.symbol);
            nbits -= node.terminalBits;
            node = root;
        }

        return baos.toByteArray();
    }

    private void buildTree() {
        for (int i = 0; i < CODE_LENGTHS.length; i++) {
            addCode(i, CODES[i], CODE_LENGTHS[i]);
        }
    }

    private void addCode(int sym, int code, byte len) {
        Node terminal = new Node(sym, len);

        Node current = root;
        while (len > 8) {
            len -= 8;
            int i = ((code >>> len) & 0xFF);
            if (null == current.children) {
                throw new IllegalStateException("invalid dictionary: prefix not unique");
            }
            if (null == current.children[i]) {
                current.children[i] = new Node();
            }
            current = current.children[i];
        }

        int shift = 8 - len;
        int start = (code << shift) & 0xFF;
        int end = 1 << shift;
        for (int i = start; i < start + end; i++) {
            current.children[i] = terminal;
        }
    }

    private static final class Node {

        /**
         * 终端节点
         */
        final Node[] children;

        /**
         * 终端节点符号
         */
        final int symbol;

        /**
         * 终端节点中表示的位数
         */
        final int terminalBits;

        Node() {
            this.children = new Node[Normal._256];
            this.symbol = 0;
            this.terminalBits = 0;
        }

        /**
         * 构造一个终端节点
         *
         * @param symbol 节点表示
         * @param bits   bits类型的Huffman长度
         */
        Node(int symbol, int bits) {
            this.children = null;
            this.symbol = symbol;
            int b = bits & 0x07;
            this.terminalBits = b == 0 ? 8 : b;
        }
    }

}
